Power lock mechanisms used in vehicles often employ an electric motor or actuator to move one or more lock levers between locked and unlocked positions. Typically, these latches are also equipped with a manual lock, typically an inside lock button and/or outside key cylinder. If the electric motor is constantly coupled with the lock lever(s) it has to be back-driven when the manual lock is operated. This adds to the effort required to actuate the manual lock and increases the noise of the locking/unlocking operation.
One solution to avoid back-driving the motor when the lock lever is manually operable is to equip the actuator with a return spring that automatically back-drives the motor to its initial position after each lock or unlock cycle. This allows for enough lost motion in the mechanism so that the next manual cycle can be performed without moving the motor. Alternatively, the lock actuator can include a clutch mechanism for disengaging the motor after each lock or unlock cycle. However, these solutions add parts, complexity, and costs to the lock actuator. For example, approximately 30% of the torque generated by the motor is often used to load the spring.
A similar problem arises in a power release application wherein, typically, a lever has to be actuated to move from a first position to a second position. For example, in a trunk release application, a motor is connected to an output arm which drives a release pall from a first position to a second position in order to release a trunk latch. In this case, the output arm is typically biased via a spring to cause the output arm to automatically return to its initial position in order to restart the sequence. Again, it would be desirable to actuate the output arm on the return stroke without having to backdrive the motor.